adds missing requires for arel and i18n, prevents Arel constant from being autoloaded (which was still seen), though it probably hides an issue related to dependencies

activerecord/lib/active_record.rb

@@ -30,6 +30,8 @@ $:.unshift(activemodel_path) if File.directory?(activemodel_path) && !$:.include
 
 require 'active_support'
 require 'active_model'
+require 'arel'
+require 'i18n'
 
 module ActiveRecord
   extend ActiveSupport::Autoload
@@ -117,4 +119,4 @@ ActiveSupport.on_load(:active_record) do
   Arel::Table.engine = Arel::Sql::Engine.new(self)
 end
 
-I18n.load_path << File.dirname(__FILE__) + '/active_record/locale/en.yml'
+I18n.load_path << File.dirname(__FILE__) + '/active_record/locale/en.yml'